Copper -- the stuff of pennies and tea kettles -- is also one of the few metals that can turn carbon dioxide into hydrocarbon fuels with relatively little energy. When fashioned into an electrode and stimulated with voltage, copper acts as a strong catalyst, setting off an electrochemical reaction with carbon dioxide that reduces the greenhouse gas to methane or methanol.

Various researchers around the world have studied coppers potential as an energy-efficient means of recycling carbon dioxide emissions in powerplants: Instead of being released into the atmosphere, carbon dioxide would be circulated through a copper catalyst and turned into methane  which could then power the rest of the plant. Such a self-energizing system could vastly reduce greenhouse gas emissions from coal-fired and natural-gas-powered plants.

But copper is temperamental: easily oxidized, as when an old penny turns green. As a result, the metal is unstable, which can significantly slow its reaction with carbon dioxide and produce unwanted byproducts such as carbon monoxide and formic acid.

Now researchers at MIT have come up with a solution that may further reduce the energy needed for copper to convert carbon dioxide, while also making the metal much more stable. The group has engineered tiny nanoparticles of copper mixed with gold, which is resistant to corrosion and oxidation. The researchers observed that just a touch of gold makes copper much more stable. In experiments, they coated electrodes with the hybrid nanoparticles and found that much less energy was needed for these engineered nanoparticles to react with carbon dioxide, compared to nanoparticles of pure copper.

A paper detailing the results will appear in the journal Chemical Communications; the research was funded by the National Science Foundation. Co-author Kimberly Hamad-Schifferli of MIT says the findings point to a potentially energy-efficient means of reducing carbon dioxide emissions from powerplants.

You normally have to put a lot of energy into converting carbon dioxide into something useful, says Hamad-Schifferli, an associate professor of mechanical engineering and biological engineering. We demonstrated hybrid copper-gold nanoparticles are much more stable, and have the potential to lower the energy you need for the reaction.

Going small

The team chose to engineer particles at the nanoscale in order to get more bang for their buck, Hamad-Schifferli says: The smaller the particles, the larger the surface area available for interaction with carbon dioxide molecules. You could have more sites for the CO2 to come and stick down and get turned into something else, she says.

Hamad-Schifferli worked with Yang Shao-Horn, the Gail E. Kendall Associate Professor of Mechanical Engineering at MIT, postdoc Zichuan Xu and Erica Lai 14. The team settled on gold as a suitable metal to combine with copper mainly because of its known properties. (Researchers have previously combined gold and copper at much larger scales, noting that the combination prevented copper from oxidizing.)

To make the nanoparticles, Hamad-Schifferli and her colleagues mixed salts containing gold into a solution of copper salts. They heated the solution, creating nanoparticles that fused copper with gold. Xu then put the nanoparticles through a series of reactions, turning the solution into a powder that was used to coat a small electrode.

To test the nanoparticles reactivity, Xu placed the electrode in a beaker of solution and bubbled carbon dioxide into it. He applied a small voltage to the electrode, and measured the resulting current in the solution. The team reasoned that the resulting current would indicate how efficiently the nanoparticles were reacting with the gas: If CO2 molecules were reacting with sites on the electrode  and then releasing to allow other CO2 molecules to react with the same sites  the current would appear as a certain potential was reached, indicating regular turnover. If the molecules monopolized sites on the electrode, the reaction would slow down, delaying the appearance of the current at the same potential.

The team ultimately found that the potential applied to reach a steady current was much smaller for hybrid copper-gold nanoparticles than for pure copper and gold  an indication that the amount of energy required to run the reaction was much lower than that required when using nanoparticles made of pure copper.

Going forward, Hamad-Schifferli says she hopes to look more closely at the structure of the gold-copper nanoparticles to find an optimal configuration for converting carbon dioxide. So far, the team has demonstrated the effectiveness of nanoparticles composed of one-third gold and two-thirds copper, as well as two-thirds gold and one-third copper.

Hamad-Schifferli acknowledges that coating industrial-scale electrodes partly with gold can get expensive. However, she says, the energy savings and the reuse potential for such electrodes may balance the initial costs.

Its a tradeoff, Hamad-Schifferli says. Gold is obviously more expensive than copper. But if it helps you get a product thats more attractive like methane instead of carbon dioxide, and at a lower energy consumption, then it may be worth it. If you could reuse it over and over again, and the durability is higher because of the gold, thats a check in the plus column.

This story is republished courtesy of MIT News (http://web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

recycling carbon dioxide emissions in powerplants: Instead of being released into the atmosphere, carbon dioxide would be circulated through a copper catalyst and turned into methane  which could then power the rest of the plant.

I guess I'm missing the point. Thermodynamics requires MORE energy to convert CO2 into methane than can be produced by converting (combustion of) methane back into CO2 and H2O. The total mass of carbon remains constant. So how does this help?

7
posted on 04/11/2012 8:37:51 AM PDT
by LucianOfSamasota
(Tanstaafl - its not just for breakfast anymore...)

This sounds really fishy to this old engineer, but I’m burdened with those old, crusty laws of thermodynamics that were formulated before the days of quantum physics and nanotechnology. Still, the prospect of oxidizing CH4 to form CO2 and H20 to release energy and then taking “relatively little energy” to convert CO2 to CH4 sounds more like a perpetual motion machine than an economically viable process.

More than likely, the cost of producing the catalyst will be higher than the energy from the hydrocarbons produced. No where in the article did they give hard numbers for the energy cost of making this catalyst. Also, there are ALWAYS problems with scaling up a lab process to a commercial operation. Things that work well on small scales sometimes have a tendency to get unstable when scaled up.

Then the amount of energy to recycle more and more carbon will eventual overwhelm the productive capacity of the plant, consuming all energy converted from combustion of new carbon based fuels. Very strange.

16
posted on 04/11/2012 8:54:21 AM PDT
by LucianOfSamasota
(Tanstaafl - its not just for breakfast anymore...)

Let’s see CO2 has one carbon atom and two oxygen atoms. Methane is CH4, that is one carbon atom and 4 hydrogen atoms. I never see in the article where the hydrogen atoms are going to come from. Besides as cheap as methane is today I don’t see the point.

I think you guys are missing something. It sounds to me like the whole article is talking about a breakthrough in combining CO2 and hydrogen, into methane. Thus its not a perpetual motion machine. The hydrogen will be supplied outside of this process. That is the only thing that make sense to me.

Actually, this is really promising. It’s true that you need to add energy to convert the CO2 to hydrocarbons, but solar cells are certainly capable of providing the current necessary to facilitate the conversion. If this technology proves feasible, it would be a great step toward energy independence.

BTW, the oxygen to burn the hydrocarbons is simply recycled back to the atmosphere when the CO2 is converted to CH4.

This process also suggests a path to create natural gas inorganically in the earth’s crust: carbonate rocks, heat, and a little hydrogen could do the trick. The difficult part is creating the hydrogen efficiently.

Any reaction converting CO2 back into methane will consume 891 kJ/mol if 100% efficient. And no process is 100% efficient. So (and thermodynamics guarantees this result, hence no 'perpetual motion' machines) converting the same chemical reaction back and forth must ALWAYS result in a net energy LOSS. I'm a physicist, not a chemist, but this is pretty basic stuff.

31
posted on 04/11/2012 9:29:20 AM PDT
by LucianOfSamasota
(Tanstaafl - its not just for breakfast anymore...)

To test the nanoparticles reactivity, Xu placed the electrode in a beaker of solution and bubbled carbon dioxide into it. He applied a small voltage to the electrode, and measured the resulting current in the solution.

I would assume the solution contains mostly water. Which would, of course, contain the necessary H for the process.

The process involves immesing the electrode in water through which CO2 is passed, so the current will break down the water molecules to obtain the hydrogen. The reaction produces 3 molecules of oxygen for each molecule of methane: 2H2O + CO2 = CH4 + 3O2

Of course you wouldn’t use methane to produce hydrogen to be used to produce methane. One of the holy grails of catalytic chemistry has been efficient water splitting. That is the best place to find hydrogen for this process. And yes, it requires energy. My point was, simply, that if solar energy could create the current necessary to power this reaction, it would be an efficient way to produce a mobile fuel.

Of course, by trapping more solar energy, we could change the earth’s heat balance and create global warming.

(BTW, I am not a warmist, but I believe it is prudent to explore as many alternate energy processes as we can. It’s just good science.)

Apart from recovering and recycling waste CO2, another angle to this process (if it is efficient enough) is that it could be another effective way to store and transport electric power. As methane, it transports nicely.

46
posted on 04/11/2012 10:13:24 AM PDT
by Ramius
(Personally, I give us one chance in three. More tea anyone?)

How much voltage, for how long? IOW, will it cost more to supply the necessary voltage than the net value of the fuel produced?

Will it end up as inefficient as the other "green" technologies?

Well, let's see...First you burn coal to make steam to turn a turbine that drives a generator that produces electricity. The process also produces CO2 which can be reacted with a copper/gold electrode in an undefined solution to produce methane (natural gas). So lets just burn the methane along with the coal, oh oh, we just produced more CO2...Back to the magic cells to make more methane.

At some point could we drop the coal altogether and just burn methane to produce electricity and CO2 while reacting the CO2 with the copper/gold electrodes and the secret sauce (with just a pinch of the electricity produced, leaving enough power to keep our customers smiling!) Let's look a little closer, we have a closed process with a fixed amount of CO2 which we convert to methane using a catalyst and electricity. We then burn the methane, extracting heat to produce electricity and more CO2 to continue the process indefinitely.

Neat! Except that the laws of physics regarding the conservation of energy require that the amount of energy needed to synthesize the methane will be greater than what you can recover by burning the same amount of as fuel. This is why all thermodynamic processes reject heat to the environment (cooling towers!!).

Lastly, converting all the CO2 produced by a coal fired power plant to methane or methanol does not destroy the gas forever, it hides it as unburnt hydrocarbons in the newly produced fuels. As soon as those fuels are burnt, presto, the same amount of CO2 is released into the environment, the energy recovered will be less then the energy input to the synthesis as electricity. And what a long strange trip it's been...

The closed box that produces perpetual energy output is just as imposable as the proverbial "free lunch".

Regards, GtG

49
posted on 04/11/2012 10:20:51 AM PDT
by Gandalf_The_Gray
(I live in my own little world, I like it 'cuz they know me here.)

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